1. Field of the Invention
The present invention relates to a light scanning device, and more particularly to a light scanning device including a light deflector for deflecting a scanning light beam employed to scan a desired surface and a synchronizing light beam employed to produce a synchronizing signal.
2. Description of the Prior Art
Recent years have seen the development of various light scanning devices for reading out and/or recording images with a light beam. In such light scanning devices, a light beam produced by a light source is reflectively deflected by a light deflector such as a rotating polygonal mirror to scan a desired object surface one-dimensionally in a main scanning direction. At the same time, the object surface is moved at a constant speed in a subscanning direction which is substantially normal to the main scanning direction, the net result being two-dimensional scanning of the object surface. These light scanning devices employ a synchronizing light beam, in addition to the above light beam for scanning the object surface (scanning light beam), to generate a synchronizing signal so that scanning distortions or irregularities in the main scanning direction can be corrected.
With the conventional light scanning devices, the scanning light beam and the synchronizing light beam are produced generally by applying one or two light beams to the light deflector, applying the light beam or beams reflectively deflected by the light deflector to a scanning lens, and then picking up the light beam or beams that have left the scanning lens at mutually conjugate planes. Where only one light beam is applied to the light deflector, the light beam having left the scanning lens is divided into two light beams by a half-silvered mirror or the like. The synchronizing light beam thus produced is then applied to a grid positioned where the synchronizing light beam is converged and extending in the main scanning direction. The light beam that has passed through the grid is detected by a light detector disposed behind the grid. Since the synchronizing light beam and the scanning light beam are converged by the same scanning lens, however, the optical paths for the synchronizing and scanning light beams are equal to each other. The scanning widths traversed by the scanning and synchronizing light beams are also equal to each other. Therefore, the grid and the light detector which are located at the converging point of the synchronizing light beam are required to have at least the same length as the main scanning width on the object surface being scanned. As a result, the light scanning devices with the means for generating the synchronizing light beam in the above manner need a space therein to establish the optical length for the synchronizing light beam. Moreover, the overall light beam scanning device is large in size because of the elongate grid and light detector.